The present invention relates to an apparatus or arrangement for duplex transmission in a radio or similar device with a transmitter and receiver, wherein the arrangement comprises a transmitter filter, a receiver filter and preferably a transmitter/receiver device which is fixedly or demountably arranged, wherein the receiver filter comprises a SAW-filter (Surface Acoustic Wave filter) and the transmitter filter and the SAW-filter are connected via a circulator.
This application claims priority from Swedish Patent Application No. 9300349-9, filed Feb. 5, 1993, which is expressly incorporated here by reference.
The filters of such an arrangement, on which the requirements are high, i.e., as far as selectivity, through-attenuation, etc. are concerned, are today large, among other reasons because of physically large resonators. Therefore, arrangements of the given kind are difficult to integrate due to their size which can be both time consuming as well as leading to increased costs. Furthermore, the products comprising said arrangement are large and cumbersome which can be of great significance for the intended application as well as its use and utilization as such. An example where it is significant that the size of such arrangements can be limited are hand-held telephones, particularly so called analog cellular pocket telephones.
Arrangements as referred to above are known. According to a known embodiment, a duplex filter is arranged between a transmitter and a receiver which have a receiver filter and a transmitter filter wherein between the filters an antenna is arranged. With known embodiments either ceramic filters or "helical" filters are used as transmitter filters as well as receiver filters. Those filters, however, have physically large resonators; as a result, the arrangement of the components will get large and difficult to integrate into customer specific circuits, such as for example ASICs (Application Specific Integrated Circuits).
These arrangements are used in, among other things, analog cellular hand-held telephones which also will be large among other reasons because the duplex filters are large. This is a drawback in portable telephones since it is essential that these are small and easy to handle in order to become really customer friendly. The requirements of the market get higher and higher in respect thereof. Even if also other factors play a role, such as, e.g., batteries, involved electronics, etc., the filter size is a very important factor.